1. Technical Field
The present invention relates generally to purge control systems for internal combustion engines and more particularly to a method for controlling a vapor storage canister for a purge control system of an internal combustion engine.
2. Discussion
Stricter Federal and California evaporative emission standards for automotive vehicles require that Federal Test Procedure (FTP) emission levels be measured with a loaded vapor canister. The standards require that the automotive vehicle undergo an FTP emission cycle, after which the vehicle is placed in a variable temperature shed and resting loss emissions re measured over a predetermined time period.
Under normal automotive vehicle operating conditions, fuel vapors present within the vehicle""s fuel tank are temporarily stored inside a vapor storage canister. These devices are known in the art as purge canisters or vapor storage canisters. A typical vapor storage canister contains a quantity of activated charcoal as the preferred medium for storing the fuel vapors. The storage capacity of the vapor storage canister is limited by the mass and volume of charcoal after becoming saturated with absorbed fuel vapor. Therefore, it is necessary to periodically purge the vapor storage canister with fresh air to remove the fuel vapor and restore the storage potential of the canister.
Typically, a purge control system is used to purge the vapor storage canister. The purge control system includes a purge solenoid which is turned ON and OFF to control fuel vapor purged from the vapor storage canister. An example of such a purge control system is disclosed in U.S. Pat. No. 4,821,701 to Nankee II et al. Another example of a purge control system for controlling and varying the amount of purge flow from the vapor storage canister to the internal combustion engine is disclosed in U.S. Pat. No. 5,263,460 to Baxter et al.
One problem associated with the use of such purge control systems is that the amount of fuel which they deliver to the internal combustion engine during a purge cycle is not quantified. Accordingly, in situations where a substantial amount of fuel vapor is being generated (e.g., where the vehicle is operating in a relatively hot environment or where the vehicle is fueled with an oxygenated fuel), operation of the purge control system in an ON condition is likely to be frequent and provide the internal combustion engine with a relatively large supply of fuel. The delivery of fuel to the internal combustion engine via the purge control system is likely to cause erratic engine operation, particularly when the vehicle is idling and a heavy load is applied to the engine, as when actuating an air conditioning compressor.
When the engine is idling and the purge control system is turned ON, for example, the additional fuel being delivered to the internal combustion engine causes a rich burn situation wherein the ratio of fuel to air is higher than a desired stoichiometric ratio. This situation is typically detected via an oxygen sensor. In response to the detection of a rich burn situation, the engine controller typically reduces the amount of fuel that is being delivered to the internal combustion through the primary fueling means (e.g., injectors) to return the fuel-to-air ratio to the desired stoichiometric ratio. In response to the application of a heavy load to the engine, the idle speed motor opens the throttle, causing the engine to ingest relatively more air and altering the fuel-to-air ratio to create a lean bun situation and reducing the available engine torque. The lean burn situation is the result of the failure to estimate or predict the quantity of fuel that is being delivered to the engine for combustion from the purge canister and the corresponding need to retard the rate with which the injectors are permitted to change the amount of fuel that is delivered to the engine so as to avoid over reacting to variances in the amount of fuel that is being delivered from the purge canister. The speed of the engine will vary widely until a sufficient amount of time has elapsed to permit the fuel-to-air ratio to return to the desired stoichiometric ratio.
Accordingly, there remains a need in the art for a device for controlling the fueling of an engine assembly which estimates the amount of fuel that is being delivered to the engine for combustion from a purge canister. There also remains a need in the art for a method of fueling an engine that more accurately accounts for the amount of fuel that is being delivered to the engine for combustion from a purge canister.
In one preferred form, the present invention provides a control system for controlling the fueling of an engine assembly. The engine assembly includes an internal combustion engine, a fuel control system, a fuel vapor storage canister and a purge control system for purging the fuel vapor storage canister. The control system includes a purge fuel vapor measuring device for measuring an amount of purge fuel vapor flowing from the vapor storage canister to the internal combustion engine, a fuel corruption estimating device for estimating an amount of fuel corruption as a function of the amount of purge fuel vapor flowing from the vapor storage canister to the internal combustion engine and a controller for adapting the control of the internal combustion to the estimate of the amount of fuel corruption. A method for fueling an engine assembly having an internal combustion engine is also provided.